Chapter 9 Stoichiometry Getting Started:
4 c. of flour
3 c. of sugar
3 eggs
1 tsp. of vanilla
2 sticks of butter
1 tsp. of salt 8 c. of chocolate chips These following ingredients at the top make 4 dozens of cookies
If you have..
20 c. of flour
15 c. of sugar
15 eggs
7 tsp. of vanilla
4 sticks of butter
5 tsp. of vanilla
30 c. chocolate chips You can only make 8 dozens of cookies because of butter. The butter is the limiting reactant.
How to do stoichiometry:
1) Get a balanced equation
2) Figure out the multiplication factor
3) Find out number of mol of what you need
4) Convert mol to g using molar mass (If must)
Example: How many moles of chlorine gas (Cl2) would react with 5 moles of sodium (Na) according
to the following chemical equation? 2Na + Cl2 --> 2NaCl Answer: 2.5 mol Cl2 Finding percent composition:
1) Find the molar mass of the compound
2) Find the percentage of each element's mass
Example: What is the percent of carbon and oxygen in CO2
1) Find the molar mass of the compound: The molar mass of CO2 is 44. C = 12, O = 16
2) Find the percentage of each element's mass. C = 12/44, O = 32/44 Answer: 27.27% Carbon, 72.73% Oxygen
Determing empirical formulas:
1) Find the number of moles of each element
2) Find the ratio of moles of each element (divide by smallest)
3) Apply the ratio to the formula
Example: 0.29 mol S, 0.435 mol O. Find the empirical formula for S and O.
1) Find the number of moles of each element: 0.29 mol S, 0.435 mol O
2) Find the ratio of moles of each element (divide by smallest): 0.29 mol S / 0.435 mol O = 1: 1.5 ratio
However since you can't have half of a mol, you have to double the ratios to get the whole number --> 2:3 ratio
3) Apply the ratio to the formula: S, O = S2O3 Answer: S2O3 (2:3 ratio)
Finding molecular formulas:
1) Find the empirical formula
2) Find the mass of empirical formula
3) Divide molecular mass (given) by the mass of the empirical formula
4) Multiply empirical formula by anser from step 3
Example: Given molecular mass: 224 g/mol. Find the molecular formula for S and O.
Molecular mass of the empirical formula: S2O3
1) Find the empirical formula: S2O3
2) Find the mass of empirical formula: 32 * 2 + 16 * 3 = 112
3) Divide molecular mass (given) by the mass of the empirical formual: 224 / 112= 2
S2O3 * 2 = S4O6 Answer: S4O6
Getting Started:
4 c. of flour
3 c. of sugar
3 eggs
1 tsp. of vanilla
2 sticks of butter
1 tsp. of salt
8 c. of chocolate chips
These following ingredients at the top make 4 dozens of cookies
If you have..
20 c. of flour
15 c. of sugar
15 eggs
7 tsp. of vanilla
4 sticks of butter
5 tsp. of vanilla
30 c. chocolate chips
You can only make 8 dozens of cookies because of butter. The butter is the limiting reactant.
How to do stoichiometry:
1) Get a balanced equation
2) Figure out the multiplication factor
3) Find out number of mol of what you need
4) Convert mol to g using molar mass (If must)
Example: How many moles of chlorine gas (Cl2) would react with 5 moles of sodium (Na) according
to the following chemical equation? 2Na + Cl2 --> 2NaCl
Answer: 2.5 mol Cl2
Finding percent composition:
1) Find the molar mass of the compound
2) Find the percentage of each element's mass
Example: What is the percent of carbon and oxygen in CO2
1) Find the molar mass of the compound: The molar mass of CO2 is 44. C = 12, O = 16
2) Find the percentage of each element's mass. C = 12/44, O = 32/44
Answer: 27.27% Carbon, 72.73% Oxygen
Determing empirical formulas:
1) Find the number of moles of each element
2) Find the ratio of moles of each element (divide by smallest)
3) Apply the ratio to the formula
Example: 0.29 mol S, 0.435 mol O. Find the empirical formula for S and O.
1) Find the number of moles of each element: 0.29 mol S, 0.435 mol O
2) Find the ratio of moles of each element (divide by smallest): 0.29 mol S / 0.435 mol O = 1: 1.5 ratio
However since you can't have half of a mol, you have to double the ratios to get the whole number --> 2:3 ratio
3) Apply the ratio to the formula: S, O = S2O3
Answer: S2O3 (2:3 ratio)
Finding molecular formulas:
1) Find the empirical formula
2) Find the mass of empirical formula
3) Divide molecular mass (given) by the mass of the empirical formula
4) Multiply empirical formula by anser from step 3
Example: Given molecular mass: 224 g/mol. Find the molecular formula for S and O.
Molecular mass of the empirical formula: S2O3
1) Find the empirical formula: S2O3
2) Find the mass of empirical formula: 32 * 2 + 16 * 3 = 112
3) Divide molecular mass (given) by the mass of the empirical formual: 224 / 112= 2
S2O3 * 2 = S4O6
Answer: S4O6
Made by. James Kim and Adam Polinak
Pictures from...
http://pulse.pharmacy.arizona.edu/11th_grade/industrialization/chemistry/images/stoichiometry.png
http://www.kcl.ac.uk/kis/schools/life_sciences/health/pharmacy/resgrps/mcrg1/MedChemGp01/images/Fecp20.jpg